The invention relates to an electrodynamic drive system.
Electrodynamic systems are suggested in various systems as assemblies between an internal combustion engine and a transmission in a vehicle. In DE 199 34 696 A1, for example, an electrodynamic drive system for a vehicle is described, which is equipped with a planetary transmission positioned between a drive engine and a manual transmission, which comprises the three elements sun gear, internal gear, and planet carrier. The planet carrier, as the first element, is connected to the manual transmission; the internal gear, as the second element, is connected to the drive engine; and the sun gear, as the third element, is connected to at least one electric motor. This assembly allows the drive engine to be started, electrical power to be generated, power braking, and the vehicle to be started from a position of rest. No special solutions for starting the drive engine under cold-start conditions are described in DE 199 34 696.
With known-in-the-art crankshaft-starter generators, the cold-start torque of the internal combustion engine must be overcome, and the device must still be capable of accelerating the rotating masses to the necessary starting speed. This means that the electric motor of the crankshaft-starter generator must generate higher levels of torque than simply the cold-start torque of the internal combustion engine. The principal disadvantage of this arrangement is that two opposing requirements, namely cold-start and generator operation, are placed upon the same electric motor at higher speeds for the internal combustion engine. In order to obtain the high mechanical torque for a cold start, the speed that corresponds to a preset output for the electric motor must be set very low. Thus, to cover the entire speed band for the internal combustion engine in the operation of the electric motor as a generator, a broad field weakness range for the electric motor is necessary. This broad field weakness range results in a poor efficiency level in generator operation at higher internal combustion engine speeds. The required high levels of torque also require high engine flow rates, resulting in high costs for the required power electronics.
With known-in-the-art pulse starters, an electric motor is connected to the crankshaft on the side of the internal combustion engine via a clutch. On the transmission side, a conventional starter coupling with a torsion damper is positioned between the electric motor and the clutch input shaft. In order to avoid the above-named disadvantages related to the electric motor and the power electronics, both couplings are opened in the pulse starters used to start the internal combustion engine. The electric motor accelerates only its own rotating mass, and once the flywheel starting speed has been reached, the clutch on the side of the internal combustion engine is closed. This way, the flywheel effect and the torque of the electric motor can be used to cold-start the internal combustion engine. The clutch on the side of the internal combustion engine must be designed to be as strong as, or even stronger than, the starter coupling on the transmission side, since during driving operation it must transmit all static and dynamic internal combustion engine torque, resulting in a heavy weight and high costs. An additional storage mass required for the intermediate storage of the friction energy of the disconnect-type clutch during a flywheel start further adds to the heavy weight of the assembly. The electric motor must have its own bearing, since it must be brought to the flywheel start speed independent of the internal combustion engine and the transmission. The additional clutch and the devices required for its operation necessitate a large overall length.
The objective of the invention is to provide a starter assembly for use under cold-start conditions, which will eliminate the above-described disadvantages.
The objective is attained with an electrodynamic drive system having the characteristic features specified in claim 2, and a method according to claim 1. Designs are the object of the sub-claims.
According to the invention, in an electrodynamic vehicle drive system comprised of an electric motor and a planetary transmission positioned between an internal combustion engine and a manual transmission with an input shaft, a frictionally engaged brake is provided to enable a controlled braking of the input shaft of the manual transmission against a stationary component of the housing. In a method that utilizes this type of drive system, first, with the transmission in neutral, the electric motor is accelerated to a speed that is principally sufficient to start the internal combustion engine. A controlled closing is effected via the brake, causing the input shaft of the manual transmission to move toward the stationary housing component. A level of torque that represents the sum of electric motor torque and rotational torque of the mass of rotating components acts upon the internal combustion engine, which will start the internal combustion engine reliably and quickly, even at low temperatures with the associated aggravated starting conditions. In one advantageous design, the brake is connected to the planet carrier of the planetary transmission, which is connected via a rigid revolving joint to the input shaft of the manual transmission. In another design, the brake is connected to a countershaft of the manual transmission, which is connected via a rigid revolving joint to the input shaft of the manual transmission.